This invention relates to screw conveyor pumps, and more particularly, to screw conveyor pumps of the type employing a flowstream of gas to facilitate transporting particular solids out of the pump.
It is well known to use screw conveyor pumps for transporting solid particulate matter such as flour, sugar, agricultural grains, dry chemical products and Portland cement. Such pumps generally require the introduction of pressurized gases forming a flowstream to facilitate the movement and suspension of the particulate solids downstream of the screw conveyor thereby preventing packing and clogging of the particulate matter. In this manner, the compressed gas is a significant factor in promoting movement of the particulate matter through the pump. The gas pressure may adversely effect the performance of the screw conveyor if not isolated from the screw since the gas pressure tends to blow back through the flights of the conveyor causing holes or voids in the stream of particulate solids being moved by the screw conveyor. Therefore, it becomes necessary to provide a seal for the screw conveyor to prevent blow back. Prior art screw conveyors have provided solutions to this problem which include varying the pitch of the flights of the screw conveyor to provide compression of the solid material thereby providing a seal; providing rotating plugs between various sections of a discontinuous screw conveyor so as to achieve seals due to the concentration of particulate matter between the sections of the screw conveyor; and using an expanding central core of the screw conveyor to provide compression of the particulate matter thereby securing a seal.
Another known approach used in conjunction with blow-back prevention seals has been the provision of a flapper valve at the terminal end of the barrel through which the screw conveyor extends. The flapper valves are generally gravity operated and close the terminal end of the barrel when the blow-back pressure exceeds the pressure due to the flow of particulate matter from the barrel. These flapper valves have caused the particulate matter to exit from the tube in a manner which causes a resistance or impediment to the flow of the particulate matter. The gravity operated flapper valves direct the exiting particulate solids downward to cause a discharge accumulation which results in decreasing the overall performance of the pump.
A further problem with prior art particulate matter pumps of the type employing pressurized flowstreams is that of preventing the gas pressure from forcing a small amount of the particulate matter into the bearings supporting the screw conveyor. Small amounts of the particulate matter can, of course, destroy the bearings after a relatively short operating period. Previous attempts to solve this problem have been relatively unsatisfactory. These attempts have included the use of special bearing seals to provide axial compression against the rotating shaft of the screw conveyor. Axial compression or sealing has proven generally unsatisfactory since the seals have a tendency to wear thereby allowing the gas pressure to force particulate matter laterally through the sealing surface into the bearings. Other prior art attempts have included supplying air pressure behind the seal which equals or exceeds that pressure in the other portions of the pump. This measure requires rather complex bearings, additional piping and pressure controls to insure that pressure in the seal will always be great enough to force any particulate matter away from the bearing. Such gas pressure seals are generally very expensive.
Accordingly, it is a general object of this invention to provide a particulate solids pump of the screw conveyor type which provides an effective blow-back seal of compacted particulate matter, which provides an innovative check valve that aids in the transportation of the particulate matter exiting from the pump, and which provides an effective and inexpensive seal against the introduction of particulate matter into the bearings of the pump.
It is an object of this invention to provide a particulate solids pump of the screw conveyor type in which an effective blow-back seal is achieved by a compacted accumulation of particulate matter formed in a sealing chamber beyond the terminal flight of the screw conveyor.
It is another object of this invention to provide a biased check valve at the terminal end of the barrel of the screw conveyor to aid in the prevention of blow back and to cause the particulate matter to exit the barrel in a manner to aid in its transportation by the flowstream of pressurized gas.
It is a further object of this invention to provide a bearing seal which provides both axial and lateral sealing against the introduction of matter along a rotating shaft.
To achieve these and other objects the present invention involves a particulate solids pump of the type having a hopper, a discharge chamber, a barrel connected from the hopper to the discharge chamber, a screw conveyor extending from the hopper into the barrel, and a drive shaft extending from the hopper for rotating the screw conveyor. The invention as it relates to a particulate solids pump of the type described includes a gas pressure distributor, a discharge chamber to create a flowstream of gas for facilitating the removal of particulate solids from the barrel and the discharge chamber, a check valve such as a flapper valve force biased toward closure of the end of the barrel in the discharge chamber and also designed to provide an effect on the particulate solids exiting the barrel to facilitate their entry into the flowstream of gas, a sealing chamber in the barrel adjacent the discharge chamber in which particulate solids are caused to accumulate and create a blow-back gas pressure seal. Further, the invention includes a unique sealing apparatus which may be used between the drive shaft and the hopper, which includes first, second and third sealing members, an annular collar carried by the drive shaft and grooves formed in the drive shaft. The first sealing member generally surrounds the drive shaft and a portion of the annular collar, and forms a portion of a packing gland reservoir. A first surface of the annular collar and a lip portion of the second sealing member including a grease retainer provide a volume therebetween in which grease may be inserted. The third sealing member adjoins the first sealing member and forms the remainder of the packing gland reservoir surrounding the grooves in the drive shaft. Packing gland material in the reservoir provides lateral and axial force to secure the seal.
The features of novelty which characterize this invention are recited with particularity in the annexed claims. The invention itself however both as to organization and method of operation together with further objects and advantages will be best understood by reference to the following brief description of the drawings and detailed description of the invention.